1. Field of the Invention
This invention relates to devices for gauging the inside diameter of piping and especially to such devices which are adapted to be dropped or pulled through a pipe.
2. Discussion of Related Art
The oil industry commonly employs various sizes of pipe and casing for the completion of an oil well. Such pipe and casing must be manufactured to exact specifications for the inside diameter. Slight variances of the inside diameter specifications can result in numerous and expensive problems to the company drilling the well.
A common device for gauging the inside diameter of a pipe or casing is referred to as a drift or rabbit. The common drift is a cylindrical shaped element produced from steel, aluminum or nylon. It has a length of approximately 25 inches with an outside diameter formed in accordance with the pipe or casing specifications with which the drift is to be used. The drift is dropped through the pipe or casing. If the drift proceeds through the pipe or casing unimpeded, the pipe or casing is deemed acceptable by industry standards. if the drift progress is impeded by trash, foreign objects or flaws in the pipe, then the pipe is rejected and returned for reworking or cleaning.
Because the standard drift is a solid element, it is necessary that a plurality of drifts be maintained for measuring various sized pipe and casing.
Further, the pipe used in oil field applications is often internally coated with an epoxy resin to improve the life of the pipe and increase the volume of fluid flow therethrough. This coating is relatively delicate and can be damaged easily. Once the coating of a section of pipe has been damaged, that section must be replaced. The removal of a damaged pipe section can be very expensive because several joints of pipe may have to be removed from the bore hole prior to gaining access to the damaged pipe section. The common steel drift can easily damage the coating of a pipe section and, for this reason, its use is not desired.
In order to overcome the potential for damage to the coating of a pipe section, drifts have been produced from softer material such as nylon and aluminum. Nylon and aluminum drifts are built in exactly the same manner as the steel drifts.
One disadvantage of nylon and aluminum drifts is that they are relatively light in weight. Lightweight drifts may become hung up on mud or other nondetrimental foreign substances which do not detract from the quality of the pipe and through which the heavier steel drift could penetrate. This can result in high quality pipe being discarded in error. Additionally, significant time can be lost in attempting to retrieve the drift from the pipe and the drift can be damaged in the process of retrieval.
Also, due to the design of the common drift, difficulties arise during the retrieval process. A retrieval tool must be attached to the drift in order to pull it from the pipe. Once the retrieval tool is attached, the drilling crew still runs the risk of drawing drilling fluid from the pipe as a result of a suction effect.
Further, drifts are often dropped from heights of as much as 85 feet. Consequently, they must be capable of withstanding considerable punishment. Nylon and aluminum drifts are too often incapable of withstanding such punishment are are thus damaged after short periods of use.
There has, therefore, developed a need for a drift which is sufficiently heavy to penetrate nonharmful debris in a pipe being measured yet is incapable of damaging the internal coating of the pipe. The ideal drift should also be universal in nature, that is, be capable of use with pipe having various internal dimensions in order that a large stock of drifts does not need to be maintained on hand. Also, the ideal drift should be capable of withstanding the severe shock developed by being dropped from large heights.
Several devices have been suggested for performing operations on the internal surface of a pipe. However, none of these devices fulfills the requirements of an ideal drift.
U.S. Pat. No. 3,456,727 to Nettles shows a rabbit-type of parafin scraper used to clean off the walls of well tubings. The scraper comprises an elongated metal mandril having a central bore through which fluid passes. A pair of scraping rings are connected about the scraper. The scraper is provided with a nose section constructed from resilient material to cushion the impact of the scraper.
U.S. Pat. No. 3,276,520 to Arnold teaches a plug which includes a fishing head for retrieval, resilient pressure cups and a weight. Arnold also provides fluid bypass holes in the device.